Shredders range in size and price from small and inexpensive units designed for a certain amount of pages, to large units used by commercial shredding services that cost hundreds of thousands of dollars and can shred millions of documents per hour. Some shredders used by a commercial shredding service are built into a shredding truck.
The general small shredder is an electrically powered device, but there are some that are manually powered, such as special scissors with multiple blade pairs and hand-cranked rotary shredders.
These machines are classified according to the size and shape of the shreds they produce. (As a practical matter, this is also a measure of the degree of randomness or entropy they conduct.) All types of shredders can range in size from standard scissors and other hand-operated devices all the way up to truck-sized shredders. There are also shredder selector sites that can help consumers choose a shredder that is appropriate for their needs.
Strip-cut shredders, the least secure, use rotating knives to cut narrow strips as long as the original sheet of paper. Such strips can be reassembled by a determined and patient investigator or adversary, as the product (the destroyed information) of this type of shredder is the least randomized. It also creates the highest volume of waste inasmuch as the strips are not compressed.
Cross-cut or confetti-cut shredders use two contra-rotating drums to cut rectangular, parallelogram, or lozenge (diamond-shaped) shreds.
Particle-cut shredders create tiny square or circular pieces. Cardboard shredders are designed specifically to shred corrugated material into either strips or a mesh pallet. Disintegrators and granulators repeatedly cut the paper at random until the particles are small enough to pass through a mesh.
Hammer mills pound the paper through a screen. Pierce-and-tear shredders have rotating blades that pierce the paper and then tear it apart. Grinders have a rotating shaft with cutting blades that grind the paper until it is small enough to fall through a screen.
There are numerous standards for the security levels of paper shredders, including:
DIN 66399, Level P-1=≤12 mm wide strips of any length, Level P-2=≤6 mm wide strips of any length, Level P-3=≤2 mm wide strips of any length or ≤320 mm2 particles (of any width), Level P-4=≤160 mm2 particles with width≤6 mm, Level P-5=≤30 mm2 particles with width≤2 mm, Level P-6=≤10 mm2 particles with width≤1 mm, Level P-7=≤5 mm2 particles with width≤1 mm.
United States Department of Defense (DoD)—Top Secret=0.8×11.1 mm ( 1/32″× 7/16″) no longer approved after 1 Oct. 2008 for U.S. government classified documents.
United States National Security Agency/CSS 02-01=1×5 mm required for all U.S. government classified document destruction starting 1 Oct. 2008.
Historically, the General Services Administration (GSA) set paper shredder guidance in the Interim Federal Specification FF-S-001169 dated July 1971, superseded by standard A-A-2599 for classified material, which was canceled in February 2000. GSA has not published a new standard since.